Various methods and devices have been proposed for filling the space between panes of insulating glass assemblies with dry or generally inert gases for the purpose of avoiding internal corrosion, condensation and the like, often associated with moist air. U.S. Pat. No. 4,369,084, for example, describes filling of the interpane space of an insulating glass assembly with sulfur hexafluoride, whereas U.S. Pat. No. 3,683,974 employs a fluorocarbon gas for the same purpose. Nitrogen is the gas of choice for this purpose in U.S. Pat. No. 2,756,467, and U.S. Pat. No. 4,393,105 discloses the use of a low heat transfer gas such as argon.
Prior art methods for replacing air with another gas in an insulating glass assembly are cumbersome and time consuming. In the above-mentioned U.S. Pat. No. 2,756,467, rubbery peripheral spacers are employed between pairs of glass panes, and hypodermic needles are forced through the spacers to withdraw air from the interpane spaces and to deliver nitrogen to the spaces. In U.S. Pat. No. 4,369,084, SF.sub.6, a heavy gas, is caused to enter the space between panes at the bottom of a glass assembly and to gradually fill the assembly from its bottom, thus displacing air. In U.S. Pat. No. 3,683,974, sealed, multi-pane glass assemblies are provided with holes through the glass panes through which a fluorocarbon gas is injected, air again being displaced from the interiors of the assemblies. In U.S. Pat. No. 4,393,105, a vacuum can either be drawn on individual multi-pane glass assemblies or the units can be assembled in an environment of vacuum or low heat-loss gas.
Modern insulating glass assemblies may employ extruded metal spacers that may be generally rectangular in cross section and that have hollow interiors. The spacers are bonded to confronting glass pane surfaces by means of adherent strips of a polymeric material such as polyisobutylene, and the spacers often have a plurality of small slots or holes in their walls that face the interpane spaces. Desiccants, such as calcium sulfate, may be placed within the hollow spacers for the purpose of absorbing moisture from the gas within the interpane space, the slots in the spacer wall permitting some diffusion of gas across the wall.
When hollow spacers of the type described above are employed, the use of the various methods of the prior art to replace air in the interpane space with argon or other gas generally does not provide good results since air that is present within the hollow spacer interiors commonly is not fully exchanged.
Moreover, the use of vacuum systems to draw air from an interpane space and the introduction of a different gas into the interpane space causes pressural forces to be exerted on the panes and spacer which can result in pane damage or spacer failures. Even small pressure differentials across a pane, acting on the large pane surface, can give rise to substantial pneumatic forces resulting in substantial bowing of the panes.